1. Field of the Invention
The present invention relates to a controller of and more particularly to a motor controller for image forming apparatus, for example, laser printers.
2. Description of the Related Art
Heretofore, in an forming of image forming apparatus, laser printers has been performed through processes such as charging, exposure, development, transfer, stripping, cleaning and fixing. Such an image forming apparatus is equipped with a charging unit, and exposure unit, a development unit, a transfer unit, a stripping unit and a cleaning unit which are sequentially arranged around a photosensitive drum as an image carrier, and equipped with a fixing unit for receiving a paper from the stripping unit; the apparatus is operated in such a manner that each image forming process is performed by driving the above-described each unit according to the rotary movement of the photo-sensitive drum to form an image on a paper (image-formed medium) fed and carried from a paper feeding cassette. Then, the paper is discharged onto a paper discharging tray.
The laser printer as described above is provided with motors such as a main motor which rotates the photosensitive drum, rotates a take-out roller for taking out a paper, and drives a carrying mechanism for carrying the paper, and a mirror motor which rotates a rotary mirror built in the exposure unit using laser beam.
Accordingly, for the motors used in the laser printer as described above, their revolution speed has been kept stable, even if load torque, source voltage and ambient temperature vary, by controlling their phase in such a manner that the phase of their frequency is synchronized with that of a stable standard frequency produced by a crystal oscillator as a standard oscillator, or in addition to the phase control, by controlling their frequency to compare with the standard frequency. Thus, a software servo control has been provided which uses a CPU to determine the difference between the phase of motor revolution frequency and a standard frequency, and the difference between the motor frequency and the standard frequency, and calculate a supply voltage to the responding motors so as to provide a stable rotating speed.
A software servo control system which controls a plurality of motors by detecting the motor revolution speed in synchronism with a FG pulse as an revolution frequency signal of different frequencies detected from a plurality of motors to compare with a standard frequency by use of an interruption processing program has a disadvantage that a CPU cannot execute the next interruption processing during execution of an interruption processing responding to frequency signal in normal operation, or before a currently-executed interruption processing is finished even if another frequency signal with a high standard frequency occurs, so that the higher standard frequency of the FG signal that the software servo control system deals with, the ratio of control delay time due to processing waiting to the revolution sampling frequency, thereby preventing servo control with a good response characteristic.